The invention relates to a configuration and a method for capacitative sensing of the rotatory motion of a rotary member, whereby the configuration has four electrodes located in one plane, an analysis unit connected to the electrodes and an electrically conducting coupling surface. The coupling surface is mounted at the rotary member, opposite to the electrodes, and is used for the capacitive coupling of the electrodes.
The electrodes include a central excitation electrode which is surrounded by the other electrodes, whereby in every position of rotation, the coupling surface is opposite to the surface of the excitation electrode and substantially covers such. Further, the coupling surface covers a portion of the surface formed by the remaining electrodes and during a rotation of the rotary member it sweeps over various sections of the surface formed by the remaining electrodes. As a result, in every position of rotation of the coupling surface, a capacitor with identical effect is formed between the excitation electrode and the electrically conducting coupling surface, on which the electric charge distributes after the excitation electrode is coupled in. This electric charge that is distributed over the coupling surface is transmitted to the electrodes surrounding the excitation electrode opposite to the coupling surface, depending on the position of rotation. As a result, a capacitor is formed between the electrodes that are opposite to the coupling surface in a certain rotatory position of the coupling surface. Electrons are induced that can be identified by a voltage signal at the electrodes.
To be able to identify the rotary position of the rotary member relative to the coupling surface time-resolved, the analysis unit has an excitation circuit connected to the excitation electrode for generating excitation pulses having a specified frequency (frequency circuit) and an analysis circuit connected to the remaining electrodes to detect the voltage signals applied to the electrodes and to compare these voltage signals.
These types of configurations for capacitative sensing are frequently used in supply meters, in particular, water flow meters, but also for voltage or gas meters in which the consumption of the consumed medium is transformed into a rotatory motion by a sampling element. This rotatory motion is then transmitted to the rotary member of the configuration by a coupling, a transmission and/or a spindle, to which the coupling surface is mounted.
In a water flow meter, an impeller wheel is most often used to capture the flow rate. The rotatory motion of the impeller wheel in the flow rate measuring device is a measure for the volume stream and can be detected by electrical properties of the rotary member in the configuration according to the invention. This is accomplished by a half-sided electrically conducting metal coating of the rotary element, which is an especially suitable coupling surface and couples capacitative with the electrodes of the sensor configuration, which are fixed.
An example for such a capacitative sensing process is described in EP 1 785 732 A1, which shows a configuration for detecting a rotation of a rotary member with an electrically conducting partial surface provided in an essentially planar surface of the rotary member and with a fixed sensor element having an excitation electrode and at least two receiving electrodes adjacent to the excitation electrode. The electrodes are opposite to the electrically conducting partial surface at a distance and can be coupled capacitative with the excitation electrode upon rotating the rotary member over the electrically conducting partial surface.
The detection tools provided in the configuration include a voltage tool for charging the excitation electrode with a voltage pulse that has a voltage greater than the voltage made available by the battery providing the operating voltage of the configuration, as well as an evaluation tool for picking up receiver signals of at least two receiver electrodes that are generated as a result of capacitive coupling because of the voltage pulse. Further, a comparison tool for generating a signal indicating the position of the partial surface relative to the receiver electrodes is provided. As a result of the intensity of the voltage pulse with which the excitation electrode is charged, interference effects from external electrical fields or field oscillations can be reduced. This makes it possible to dispense with the corresponding electronics in a capacitor electrode that is described in a similar configuration according to EP 1 033 578 81.
According to the teaching of EP 1 785 732 A1, two different positions of the rotary member can be detected with two electrodes. To be able to detect the direction of rotation, however, four different positions of the rotary member must be identified. For this, four receiver electrodes are required.
The detection of the voltage signals of these four electrodes requires a higher degree of complexity of the electronics and a comparably large installation space for the electrodes and the connection lines leading to the evaluation electronics. But precisely this installation space is often not available when using the configuration according to the invention in a supply meter, because the installation space in supply meters is limited.